This invention relates to a method of generating a diamond containing material (DCM).
Diamond-containing material (DCM) used extensively in cutting, milling, grinding, drilling and other abrasive operation, may take many forms, for example:                a diamond matrix tool material, where the diamond particles are held together in a metallic or intermetallic matrix. These are typically formed at atmospheric pressure by sintering together the diamond-matrix mixture, and are generally characterised by diamond volume contents that are less than 70 volume %.        abrasive compacts, that consist of a mass of ultrahard particles, typically diamond, bonded into a coherent, polycrystalline conglomerate. The abrasive particle content of these abrasive compacts is high, generally in excess of 70 volume %; and more typically in excess of 80 volume %. There is generally an extensive amount of direct particle-to-particle bonding or contact. Abrasive compacts are generally sintered under high pressure, high temperature (HpHT) conditions at which the diamond is crystallographically or thermodynamically stable. Diamond compacts are also known as PCD.        
Abrasive compacts also usually have a second or binder phase. In the case of certain types of polycrystalline diamond compacts, this second phase is typically a metal such as cobalt, nickel, iron or an alloy containing one or more such metals. Examples of composite abrasive compacts can be found described in U.S. Pat. Nos. 3,745,623; 3,767,371 and 3,743,489.
When diamond particles are combined with a suitable metallic solvent/catalyst, this solvent/catalyst promotes diamond-to-diamond bonding between the diamond grains, resulting in an intergrown or sintered structure. This mechanism occurs in part because of the solubility of carbon in the solvent/catalyst which allows carbon from the diamond to dissolve and re-precipitate on other diamonds while in the diamond stable field during manufacture. This results in extensive diamond-to-diamond bonding, hence producing a strong diamond composite. In the final sintered structure however, solvent/catalyst material necessarily remains within the interstices that exist between sintered diamond grains.
A well-known problem experienced with this type of PCD compact however, is that the residual presence of solvent/catalyst material in the microstructural interstices has a detrimental effect on the performance of the compact at high temperatures. This decrease in performance under thermally demanding conditions is postulated to arise from two different behaviours of the compact. One is related to the differences between the thermal expansion characteristics of the interstitial solvent/catalyst and the sintered diamond network; which can cause micro-cracking when the material is heated above about 400° C. This micro-fracturing significantly reduces the strength of the bonded diamond of increased temperatures.
Additionally, the solvent/catalyst metallic materials which facilitate diamond-to-diamond bonding under high-pressure, high-temperature sintering conditions can equally catalyse the reversion of diamond to graphite at increased temperatures and reduced pressure with obvious performance consequences. This particular effect is mostly observed at temperatures in excess of approximately 700° C.
As a result, PCD sintered in the presence of a metallic solvent/catalyst, notwithstanding its superior abrasion and strength characteristics must be kept at temperatures below 700° C. This significantly limits the potential industrial applications for this material and the potential fabrication routes that can be used to incorporate them into tools.
Potential solutions to this problem are well-known in the art. One type of approach focuses on the use of alternative or altered sintering aid materials. These materials when present in the final sintered structure exhibit much reduced retro-catalytic efficacy at high temperatures and typically have thermal expansion behaviours better matched with those of the sintered diamond phase.
One of the methods of altering the binder phase material is through the use of complex metallic systems that can still facilitate a consolidation of the diamond compact but have reduced thermal degradation effects in the final product. Certain classes of intermetallics are examples of these. Intermetallic compounds are typically defined as solid phases that contain two or more metallic elements, with optionally one or more non-metallic elements, whose structure is distinct from that of any of the constituents. They usually have a characteristic crystal structure and usually a definite composition. In common use the research definition, including poor metals (aluminium, gallium, indium, thallium, tin and lead) and metalloids (silicon, germanium, arsenic antimony and tellurium), is extended to include compounds such as cementite, Fe3C. The latter compounds, sometimes termed interstitial compounds can be stoichiometric, and share similar properties to the classical intermetallics.
U.S. Pat. No. 4,793,828 describes a diamond compact with a matrix phase that consists of silicon and/or silicon carbide. This compact is produced by infiltration from a silicon powder or foil source at elevated pressures and temperatures. This compact was found to be capable of withstanding temperatures of 1200° C. under a vacuum or in a reducing atmosphere without significant graphitisation or evidence of thermal degradation occurring.
U.S. Pat. No. 4,534,773 teaches the formation of a diamond compact with a binder phase comprising nickel silicides. This intermetallic binder phase is generated through the interaction/reaction between molten nickel and silicon at HpHT conditions. The material produced is claimed to be an improved thermally stable polycrystalline diamond compact.
U.S. Pat. No. 4,789,385 teaches silicon, silicon-nickel, and silicon-cobalt combinations that will form intermetallics during sintering such as silicon carbide or nickel silicides or cobalt silicides while bonding diamond in the diamond stable field. These silicides are stated to provide thermal stability to the polycrystalline diamond compact.
US 2005/0230156 revisits this topic of intermetallics with a focus on cobalt silicide (CoSi), and particularly cobalt disilicide (CoSi2). It is claimed that these compounds, formed in situ, improve thermal stability behaviour due to having a lower thermal expansion coefficient than the cobalt metal binder commonly used. It is to be noted that this patent relies on consumption of SiC to form these intermetallics; and that certainly in the case of the disilicide, the reaction is not likely to proceed for thermodynamic reasons. The use of silicide intermetallics as binders for DCM's can have significant disadvantages. Silicides are known to be very brittle and can be a source of micro-cracking and flaws when used in an environment which is impact-prone, such as drilling or machining. The patent further discloses the proposed use of other intermetallics or alloys such as cobalt aluminides, borides, niobides, tantalides etc.
Whilst many of these intermetallic modified/alternative binder systems exhibit significantly increased thermal stability of the overall composite material with respect to diamond, a problem with their use in PCD materials comes from their inability to effect the appreciable diamond-to-diamond bonding that is characteristic of conventional metal solvent/catalysts. PCD materials manufactured using intermetallic-based systems therefore tend not to perform as optimally or effectively in certain demanding abrasive applications as the standard PCD materials; albeit that they exhibit improved thermal stability.